The term broadband covers a host of new products, technologies, services, and networks. One way to define broadband networks is to categorize them as those networks that support services requiring bit rates well above one megabits per second. Business and residential subscribers will be connected to broadband networks via a common access, operating at 150 megabits per second or above, that can handle a range of different broadband service types. ATM (asynchronous transfer mode) has been chosen as the communication principle on which broadband networks will be based. A future broadband ISDN (integrated services digital network) will offer the flexibility needed to handle diverse services ranging from basic telephone service to high speed data transfer, videotelephony, and high quality television distribution. The key to this flexibility is ATM which carries digital information in special cells. This allows the network to be used efficiently by applications and services with widely differing bandwidth requirements and call characteristics.
A growable packet switching arrangement disclosed in a paper by K. Y. Eng et al., entitled "The Growable Switch Architecture: A Self-Routing Implementation for Large ATM Applications", International Conference on Communications, June 1991, has been proposed for use in ATM applications. In the disclosed arrangement, a partition is made between a front-end distribution network and a column of output packet switching modules. The outputs are divided into groups of n lines each. All incoming cells are routed through the front-end distribution network for substantially instantaneous delivery based on their destination output group addresses. As such, the distribution network must not buffer full cells and must instead perform its routing function for all the cells arriving in each packet time slot. Since the N outputs are grouped into n lines each, there are a total of N/n output groups. For each output group, the corresponding output packet switching module has m(m&gt;=n) inputs, meaning that up to m cells can be accepted for that output group in each time slot. The output packet switching module has buffers for storing full received cells. In an L.times.N packet switch, up to L cells can arrive simultaneously for a particular output group so the design range of m is n&lt;=m&lt;=L. According to the generalized knockout principle, it is possible to pick m&lt;&lt;N to yield an arbitrarily small cell loss probability that is acceptable for the switching system design, even under the most general traffic assumptions. The maximum number of cells accepted into each output group is restricted to m; if there are more than m cells destined to the same output group in a time slot, the excessive cells are simply dropped.
A first example of a growable packet switching arrangement is disclosed in the above-referenced Eng et al. paper. The distribution network is partitioned into a sorting network and a second stage of banyan-type routing elements called modified banyans. The interconnect pattern between the sorting network and the modified banyans is a perfect shuffle. A serious problem with this first growable packet switching arrangement relates to the number of stages required when the sorting network is implemented as a plurality of stages of 2.times.2 nodes. In that important case, the sorting network must have at least [log.sub.2 (max(L,N))].sup.2 /2 node stages. For reasonable values of L=1024 and N=1024, at least 50 node stages are required for the sorting network alone.
A second example of a growable packet switching arrangement is disclosed in U.S. Pat. No. 5,093,743 issued to K. Eng et al. on Mar. 3, 1992. A distribution network is constructed from a plurality of fixed wavelength transmitters which are used to transmit arriving data packets through a star coupler, and a plurality of tunable receivers which tune to whatever frequency is necessary to receive the desired data from the star coupler. A control network, constructed from a plurality of fixed wavelength receivers and a plurality of tunable transmitters, determines what frequencies the tunable receivers should tune to, and sends a signal to effectuate such tuning. With the second growable packet switching arrangement, the value of L is seriously limited due to the tunability of the receivers. An arrangement with L=1024 is not practical with existing technology. Since all the input signals are combined and transmitted to all the receivers, and since each receiver selectively receives only one frequency, there is a large power loss in transmitting a packet through the second arrangement. This results in low signal/noise ratios and corresponding high bit error rates.